Emission uniformity studies of gyrotron MIG cathodes

Recent studies indicate that unwanted mode competition is often generated in a gyrotron due to nonuniform emission of electrons from the thermionic cathode used in MIG electron guns. This mode competition significantly decreases the microwave efficiency of the device. Therefore, to reduce mode competition and improve gyrotron efficiency, a good understanding of the uniformity of emission from the cathode surface is necessary. This uniformity may be described in terms of the work function of the emitter. In this study, we determine the comparative work function quality of several gyrotron cathodes through the use of simple measurement techniques. Moreover, we attempt to define and quantify the local and global amounts of work function spread for each of these cathodes.